In semiconductor devices, electronic devices, and optical devices such as photonic crystals, multilayer thin-film structures and submicrometer order (approximately in the range of from 0.1 μm to less than 1 μm) fine pattern structures are fabricated by processing a semiconductor wafer surface or the like. In semiconductor quantum devices, for example, ultrafine particles and thin lines on the order of nanometers, which are called quantum dots and quantum wires, are fabricated and arranged on the surface of a substrate. The size and surface roughness of the fine structures (thin film structures, pattern structures, and relief structures formed by an arrangement of ultrafine particles) in these devices are important factors that determine the performance of the devices. Therefore, high fabrication precision is demanded in the formation of fine structures.
The precision of the fine structures depends on the precision of fabrication techniques used in the film formation process, etching process, and the like. However, it is not easy to form a fine structure with a fabrication precision of up to a few nanometers. The devices formed through the film formation process, etching process, and the like are generally formed by fabricating a great number of chips on a wafer surface, and it is difficult to fabricate uniform fine structures across the wafer surface. In order to solve these problems, a process to enhance the precision of the structures (such as a surface smoothing process) is performed on the fabricated fine structures as post-processing.
An example of such a surface smoothing technique is a technique of smoothing a side wall of a pattern structure or the like by a gas cluster ion beam irradiation, disclosed in International Publication No. WO2005/031838 (Patent literature 1).